1. Field of the Invention
The present invention relates to a semiconductor module device having a desired electric circuit constituted by combination of plural semiconductor devices formed on circuit boards and, more specifically, to a three-phase AC motor control module device which can be greatly improved in efficiency and reliability.
2. Description of the Related Art
Conventionally, a three-phase AC motor control module device is the most commonly used among several tens of types of semiconductor module device and serves as an inverter. FIG. 1 shows a circuit arrangement of the three-phase AC motor control module device.
Referring to FIG. 1, the module device comprises six device sections having six IGBTs (Insulated Gate Bipolar Transistors) T1 to T6 and six diodes D1 to D6, respectively. In these device sections, the collectors of the IGBTs T1 to T6 are connected to their corresponding cathodes of the diodes D1 to D6, and the emitters of the IGBTs are connected to their corresponding anodes of the diodes.
In the device sections arranged alongside an input power terminal P (hereinafter referred to as P-side device sections), the collectors of the IGBTs T1 to T3 are connected in common to the input power terminal P. In the device sections arranged alongside an input power terminal N (hereinafter referred to as N-side device sections), the emitters of the IGBTs T4 to T6 are connected in common to the input power terminal N. The emitter of the IGBT T1 of the P-side device section and the collector of the IGBT T4 of the N-side device section are connected to each other, and this connecting point is connected to an output power terminal U. The emitter of the IGBT T2 of the P-side device section and the collector of the IGBT T5 of the N-side device section are connected to each other, and this connecting point is connected to an output power terminal V. The emitter of the IGBT T3 of the P-side device section and the collector of the IGBT T6 of the N-side device section are connected to each other, and this connecting point is connected to an output power terminal W. Gate terminals G1 to G6 for issuing gate signals are connected to the gates of the IGBTs T1 to T6, respectively.
The module device having the above circuit arrangement is likely to require higher and higher power. For example, a module device used in an electric automobile needs a current capacity of 600 to 800 A. Usually, a high-power module device includes a plurality of IGBT pellets and a plurality of diode pellets connected in parallel. A plurality of pairs of IGBT and diode pellets are formed on each device section, thereby satisfying the current capacity.
FIGS. 2A and 2B schematically show a configuration of a high-power module device. In this module device, each of the IGBTs T1 to T6 shown in FIG. 1 is constituted by five IGBT pellets t, and each of the diodes D1 to D6 shown therein is constituted by ten diode pellets d. In other words, both a group of five IGBT pellets t and a group of ten diode pellets d are arranged in parallel to each other to constitute one device section.
The high-power module device shown in FIGS. 2A and 2B will be described more specifically. Three DBC (Direct Bond Copper) circuit boards 102 are soldered onto a body of a heat radiation plate 101. Two device sections each having five IGBT pellets t and ten diode pellets d are arranged in parallel on each of the DBC circuit boards 102. The IGBT and diode pellets t and d are bonded to the electrodes (collector electrodes C, emitter electrodes E, gate electrodes G) formed on each DBC circuit board 102, by means of aluminum wires 103. In this module device, a pair of P-side and N-side device sections is formed on each DBC circuit board 102. For example, as shown in FIG. 2A, the P-side device section of IGBT T1 and diode D1 and N-side device section of IGBT T4 and diode D4, the p-side device section of IGBT T2 and diode D2 and N-side device section of IGBT T5 and diode D5, and the P-side device section of IGBT T3 and diode D3 and N-side device section of IGBT T6 and diode D6 are formed on the respective DBC circuit boards 102.
The DBC circuit boards 102 are surrounded by a resin case 104 adhered to the heat radiation plate 101. A resin cover 107 is fixed onto the resin case 104 so as to cover the upper surfaces of the DBC circuit boards 102. Externally leading power terminals 105 and 106 (corresponding to the input power terminals P and N) are integrally formed in the central part of the cover 107. Output power terminals U, V and W are also attached to the cover 107 (not shown in FIG. 2B). Further, a plurality of screw holes 108 for mounting the module device, are formed outside the resin case 104 on the heat radiation plate 101.
In the module device having the above configuration, externally leading electrodes (not shown) of the DBC circuit boards 102 have to be electrically connected to one another in order to connect the respective device sections and the externally leading power terminals 105 and 106. Conventionally, this connection is attained by metallic jumper wires (not shown) or by elongating the externally leading power terminals 105 and 106. However, in the module device described above, the externally leading power terminals 105 and 106 are located in substantially the central part of the module device, though the DBC circuit boards 102 are arranged in a row. Therefore, the distances between the power terminals 105 and 106 and the respective pellets t and d vary from one another, resulting in a difference in electrical resistance and inductance between the pellets t and d. If the connection of the externally leading electrodes between the DBC circuit boards 102 is performed by elongating the power terminals 105 and 106, the module device is increased in size and accordingly the power terminals are increased in length. As a result, the electrical resistance and inductance between the power terminals 105 and 106 and each of the DBC circuit boards 102, is heightened.
The conventional module device as described above has to be improved in efficiency and reliability since it has the drawback wherein, when the externally leading power terminals 105 and 106 are extracted together from one spot of the module device, the electrical resistance and inductance between the externally leading power terminals 105 and 106 and each of the circuit boards 102 are increased, and a difference in electrical resistance and inductance occurs between the respective pellets. In particular, the high-power module device is influenced by its internal electrical resistance and inductance, in view of electrical characteristics. If the electrical resistance and inductance increase, the efficiency of the pellets is lowered, thereby causing a malfunction in a signal system.
Furthermore, since, in the conventional module device, the DBC circuit boards 102 are shaped rectangularly, stress is easy to concentrate upon those angular portions of the DBC circuit boards 102 which are in the vicinity of the screw holes 108. Therefore, the device has a drawback of easily causing a crack in the DBC circuit boards 102 when it is fastened by an air driver.